Method For Operating an Internal Combustion Engine

ABSTRACT

In a method for operating an air-compressing fuel-injection internal combustion engine having an exhaust gas post-treatment system with a particle filter and a nitrogen oxide reduction catalytic converter, a plurality of internal combustion engine operating settings are provided, each having respective predefined values for predefined internal combustion engine operating parameters. A heating operating setting is set when the internal combustion engine is warming up, while a basic operating setting is set in the warmed-up, while a basic operating setting is set in the warmed-up state. When the temperature in the exhaust gas system exceeds a predefinable first value, the heating operating setting is changed over to the basic operating setting. In the warmed-up state, at least one further, (third) operating setting, with an exhaust gas recirculation rate that is reduced compared to the basic operating setting, is provided in addition to the basic operating setting.

BACKGROUND AND SUMMARY OF THE INVENTION

This application is a national stage of PCT International ApplicationNo. PCT/EP2006/008509, filed Aug. 31, 2006, which claims priority under35 U.S.C. §119 to German Patent Application No. 10 2005 045 294.9, filedSep. 22, 2005, the entire disclosure of which is herein expresslyincorporated by reference.

The invention relates to a method for operating an air-compressingfuel-injection internal combustion engine having an exhaust gaspost-treatment system with a particle filter and a nitrogen oxidereduction catalytic converter, in which a plurality of internalcombustion engine operating settings are possible, with respectivepredefined values for predefined internal combustion engine operatingparameters.

German patent document DE 101 55 339 A1 discloses a method for operatingan internal combustion engine in which the coolant is heated rapidly bya heating operating setting, so that sufficient heat is quicklyavailable for heating the passenger compartment. The method comprisessetting internal combustion engine operating parameters which for themost part degrade the thermodynamic efficiency and cause a comparativelyhigh release of heat. However, aspects relating to the emission ofpollutants and to the consumption of fuel are not taken into account.

German patent document DE 103 23 245 A1 also proposes an operatingsetting with poor thermodynamic efficiency in order to increase theexhaust gas temperature of an internal combustion engine. The associatedproposed measures are aimed in particular at heating an oxidationcatalytic converter arranged in the exhaust gas system in the internalcombustion engine, so that said oxidation catalytic converter can betterconvert pollutants. In this context, aspects which relate to theconsumption of fuel are also largely left unconsidered.

One object of the present invention is to provide a method for operatingan air-compressing fuel-injection internal combustion engine which, onthe one hand, permits low emission of pollutants, while at the same timepermitting low fuel consumption.

This and other objects and advantages are achieved by the methodaccording to the invention for operating an air-compressingfuel-injection internal combustion engine, which is aimed, in terms ofthe emission of pollutants, in particular at low emission of particlesand low emission of nitrogen oxide. For this purpose, an exhaust gaspost-treatment system having a particle filter and a nitrogen oxidereduction catalytic converter is provided for the internal combustionengine. In order to achieve, on the one hand, optimum operation of theexhaust gas post-treatment system and, on the other hand, lowconsumption of fuel, a plurality of internal combustion engine operatingsettings with respective predefined values for predefined internalcombustion engine operating parameters are provided. When the internalcombustion engine warms up, a heating operating setting is set, and inthe warmed-up state, (i.e., after warming up has taken place), a basicoperating setting is set. The heating operating setting ensures thatcatalytic exhaust gas cleaning components, (in particular the nitrogenoxide reduction catalytic converter) in the exhaust gas post-treatmentsystem quickly reach their operating temperature.

In this context, the basic operating setting is made more favorable interms of consumption compared to the heating operating setting. If apredefinable first temperature threshold value in the exhaust gaspost-treatment system is exceeded, the system changes from the heatingoperating setting to the basic operating setting. The upward crossing ofthe first temperature threshold value preferably characterizes aready-to-operate state of an exhaust gas catalytic converter (inparticular, of the nitrogen oxide reduction catalytic converter). Thisprocedure shortens the warming up phase which is critical in terms ofthe emission of pollutants, therefore keeping the total pollutantsgenerated in the warming up phase low. On the other hand, it is ensuredthat the heating operating setting, which is unfavorable in terms ofconsumption, is maintained for no longer than necessary. As a result,the additional consumption caused by the heating operating setting isminimized.

According to the invention, in the warmed-up state, at least onefurther, in particular a third, operating setting with an exhaust gasrecirculation rate which is reduced compared to the basic operatingsetting is provided in addition to the basic operating setting.

An operating setting of the internal combustion engine within themeaning of the invention is characterized by a set of internalcombustion engine operating parameters which determine the profile ofthe combustion of fuel in a combustion chamber or chambers of theinternal combustion engine. Such internal combustion engine operatingparameters can be set largely and/or mainly independent of the loadrotational speed state of the internal combustion engine.

The internal combustion engine operating parameters which are decisivein terms of the combustion profile relate to the supply of both air andgas, as well as the supply of fuel to the combustion chambers. Inparticular, the internal combustion engine operating parameters whichare decisive for an operating setting comprise the degree of exhaust gasrecirculation, the degree of cooling of the recirculated exhaust gasand/or of the charge air of a supercharging unit and its charge airpressure, and the control of air movements in the combustion chamber,particularly in terms of turbulence in the form of swirl. In addition,the number, start and duration of fuel injection processes as well asthe fuel injection pressure which is set in the context are alsoincluded, as are control times and/or the stroke of valves whichdetermine the gas exchange and the compression ratio. The components andactuators which are necessary for this purpose are, insofar as they arenecessary, to be considered as parts of the internal combustion enginehere.

As far as the exhaust gas post-treatment system is concerned, inprinciple any component which is suitable for removing constituents ofexhaust gas in the form of particles can be used as the particle filter.For example, what are referred to as wall flow filters, sintered metalfilters, depth filters or open filter systems can be used, and acatalytic coating is advantageous in this context. The nitrogen oxidereduction catalytic converter can be, in particular, what is referred toas an SCR catalytic converter based on vanadium pentoxide and/or a noblemetal. However, it is also possible to use a nitrogen oxide storagecatalytic converter and/or nonselective, or less selective, denoxcatalytic converters. The exhaust gas post-treatment system preferablycomprises further catalytic cleaning units. An oxidation catalyticconverter, preferably in a position close to the engine, is particularlypreferred.

Warming up within the sense of the present method is understood to meanthe operating phase after the internal combustion engine starts until acomponent temperature and/or operating resource temperature whichcharacterizes warming up is reached. This is preferably a temperaturethreshold value in the exhaust gas post-treatment system.

In the third operating setting according to the invention, therelatively high exhaust gas recirculation rates of approximately 50% to60% (which are preferably provided for the basic operating setting) arereduced by approximately 10% to 40%, so that in the third operatingsetting exhaust gas recirculation rates of approximately 10% to 45% arepreferred.

The third operating setting can be configured here for further improvingthe consumption of fuel. For this purpose, in addition to the reductionin the exhaust gas recirculation rate to approximately 25%, preferablyone or more further internal combustion engine operating parameters(such as, for example, the start of a fuel main injection and/or thefuel injection pressure) are correspondingly adapted. A start of thefuel main injection which is earlier compared to the basic operatingsetting is typically set. In particular, in a third operating settingwhich is configured to be optimum in terms of consumption it isadvantageous if the injection pressure is raised by approximately 50 barto 500 bar compared to the basic operating setting which is lessfavorable in terms of consumption. Possible worsening of the rawemissions from the engine which are associated with this change does notaffect the total emissions (exhaust end pipe emissions) because theexhaust gas post-treatment system is then fully functionally capable.

However, the third operating setting can also be configured to heat theexhaust gases. With this configuration, in addition to reducing theexhaust gas recirculation rate (in this case, by approximately 10%), oneor more further internal combustion engine operating parameters arepreferably also adapted compared to the basic operating setting. In thisrefinement, cooling of exhaust gas cleaning components which hasoccurred or threatens to occur due, for example, to unfavorable travelstates, can be avoided or eliminated by the third operating setting, sothat their functional capability is not adversely affected. An exhaustgas recirculation rate of approximately 45% to 55%, and therefore anonly slightly smaller exhaust gas recirculation rate than in the basicoperating setting, is preferably set. In addition, it is advantageousfor application of heat to the exhaust gas to add a late fuelpost-injection with a start of injection at approximately 60° CAaTDC to160° CAaTDC (degrees of crank angle after the top dead center), whereaspreferably no post-injection is provided for the basic operatingsetting.

In one refinement of the invention, the internal combustion engine isoperated with a compression ratio of less than 19:1, at least in one ofthe combustion methods which are set in the warmed-up state. Theinternal combustion engine is preferably operated with a compressionratio of less than 18:1 and particularly preferably of less than 17:1.The compression ratio may be variable in this context, but it ispreferably permanently predefined owing to the geometries and is of thesame size for all cylinders of the internal combustion engine. Due tothe comparatively low compression ratio for an air-compressing internalcombustion engine, it can be operated with particularly low rawemissions of nitrogen oxide. The nitrogen oxide reduction catalyticconverter can therefore operate particularly effectively, so thatcorrespondingly low nitrogen oxide emission values are made possible forthe exhaust end pipe emissions. If appropriate, the nitrogen oxidereduction catalytic converter can also be made smaller and thereforemore cost effective than in internal combustion engines which areoperated with a relatively high compression ratio. A relatively smallnitrogen oxide reduction catalytic converter also exhibits improvedwarming up behavior and is easily accommodated in the exhaust gassystem. The nitrogen oxide reduction catalytic converter then preferablyhas a catalytic converter volume which is less than three times,particularly preferably less than twice, the cubic capacity of theinternal combustion engine.

In a further refinement of the invention, the first temperaturethreshold value characterizes a start of the effectiveness of thenitrogen oxide reduction catalytic converter, and an additive fornitrogen oxide reduction is added to the internal combustion engineexhaust gas in the warmed-up state upstream of the nitrogen oxidereduction catalytic converter. A temperature is preferably sensed in thebed of the catalytic converter or at the inlet end of the nitrogen oxidereduction catalytic converter and compared with a respective, storedreference value which correlates with or corresponds to what is referredto as the light-off temperature of the nitrogen oxide reductioncatalytic converter. In this context the stored reference value can beadapted continuously or from time to time in accordance with an agingstate of the nitrogen oxide reduction catalytic converter. If thereference value is exceeded, the combustion method is changed over, anenable signal for the supply of the additive is set and, if appropriate,the supply is started immediately. The nitrogen oxide reductioncatalytic converter is preferably embodied as an SCR catalytic converterand the additive is ammonia, urea or some other substance which iscapable of releasing ammonia.

In a further refinement of the invention, when the heating operatingsetting is active and a predefinable second temperature threshold valueis exceeded in the exhaust gas post-treatment system, a separate fuelpost-injection is activated. The other internal combustion engineoperating parameters of the heating operating setting preferably remainunchanged. This is therefore a variant of a heating operating settingwith an additional fuel post-injection. The activated fuelpost-injection is preferably configured as a late, fuel post-injectionwhich does not also burn and has a start of injection of approximately140° CAaTDC. Therefore with this refinement of the method, the internalcombustion engine first operates without late post-injection immediatelyafter it starts with the heating operating setting active. The latepost-injection is activated only when the second temperature thresholdvalue is exceeded.

It is advantageous here if, immediately after the internal combustionengine starts, an early, accumulated post-injection which also burns iscarried out and is also maintained after the late post-injection isactivated. When the late post-injection is activated, a certain degreeof warming up has already taken place so that condensable componentswhich have possibly entered the exhaust gas through the post-injectionare prevented from becoming deposited and raised hydrocarbon exhaust endpipe emissions are avoided.

In a further refinement of the invention, the second temperaturethreshold value characterizes the start of the effectiveness of anoxidation catalytic converter connected upstream of the particle filter.The temperature in the bed of the catalytic converter and/or at theinlet end of the oxidation catalytic converter is preferably sensed andcompared with a stored respective reference value which correlates withthe light-off temperature of the oxidation catalytic converter orcorresponds to it. The unburnt components in the oxidation catalyticconverter which are introduced into the exhaust gas when a latepost-injection is activated and the heating operating setting is active,can therefore be converted. As a result, the application of heat intothe exhaust gas rises so that even exhaust gas cleaning units which arearranged further away from the engine are quickly heated up.

In order to ensure that unburnt exhaust gas components in the oxidationcatalytic converter are converted over the running time, that the storedreference value can be adapted, continuously or from time to time, inaccordance with the aging state of the oxidation catalytic converter. Ifthe reference value is exceeded, the late fuel post-injection isactivated.

In a further refinement of the method, when either the heating operatingsetting or the basic operating setting is active, the fuel injectioncomprises at least one separate pre-injection. A separate pre-injectionwhich is positioned in terms of timing before the main injection ensuresstable combustion. This is advantageous both with respect to the latepost-injection which is carried out in the heating operating setting andwith respect to a low compression ratio.

Further stabilization of the combustion is achieved if, in a furtherrefinement of the method, at least when the basic operating setting isactive, double fuel pre-injection is performed.

In a further refinement of the method, when the heating operatingsetting is active, a fuel injection pressure which is reduced comparedto the basic operating setting is set. This measure permits a furtherincreased application of heat into the exhaust gas, thereby furtherincreasing heating up speed of the exhaust gas post-treatment system,with simultaneously reduced NOx raw emissions.

In a further refinement of the method, when a third operating setting isactive, an increased fuel injection pressure (compared to the basicoperating setting) is set, so that an improved combustion in thecombustion chambers can be achieved. The increase compared to the basicoperating setting is typically between 50 bar and 500 bar. The ratedinjection pressure which is provided for the fuel injection system istherefore typically achieved under full load and at increased rotationalspeeds.

In a further refinement of the method, in the warmed-up state, afurther, fourth operating setting is also performed, in which, whenthere is a changeover from the basic operating setting or from the thirdoperating setting into the fourth operating setting, a late fuelpost-injection is activated and/or the exhaust gas recirculation rate isreduced. The third operating setting is configured here to be optimizedin terms of consumption, while the fourth operating setting facilitatesheating the exhaust gas. Apart from the activated fuel post-injection orthe reduced exhaust gas recirculation rate, the other internalcombustion engine operating parameters of the basic operating settingpreferably remain unchanged.

In a further refinement of the method, at least in one of the operatingsettings which is provided in the warmed-up state, an at least temporaryinlet duct deactivation is provided. This measure is preferably carriedout in a low load range (with less than approximately 50% of the ratedload). However, at comparatively low rotational speeds the inlet ductdeactivation can also be provided in the entire load range. Thedeactivated inlet duct is preferably what is referred to as a fillingduct, while the non-deactivated inlet duct is preferably what isreferred to as a swirl duct. Deactivating the filling duct achieves anincreased swirl of the supply of gas and therefore better combustion,lower emission of particles and lower consumption of fuel. Thedeactivation of an inlet duct is preferably performed continuously asthe load decreases.

In a further refinement of the method, at least in one of the operatingsettings which is provided in the warmed-up state, a glow plug which isassigned to a combustion chamber of the internal combustion engine isheated, at least temporarily. This measure is preferably also performedin a partial load range of the internal combustion engine and/or whenthe external temperature is low. As a result, the injected fuel isreliably ignited and therefore low HC raw emissions and low consumptionof fuel are achieved. This is advantageous in particular in conjunctionwith a low compression ratio.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an advantageous embodiment of aninternal combustion engine for carrying out the method according to theinvention;

FIG. 2 is a preferred embodiment of an exhaust gas post-treatment systemfor carrying out the method according to the invention;

FIG. 3 is a schematic state diagram of a preferred sequence of themethod according to the invention; and

FIG. 4 is a timing diagram with exemplary temperature profiles forvarious operating settings together with an associated travel curve.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically an internal combustion engine 1 for a motorvehicle (not shown), which is provided for carrying out the methodaccording to the invention, with particular consideration of the supplyof gas. The internal combustion engine 1 is preferably embodied as adirect-injection, air-compressing internal combustion engine with a lowcompression rate. An assigned injection system (not shown) is preferablyembodied as a common rail system with an adjustable rail pressure orfuel injection pressure.

The internal combustion engine 1 has a plurality of cylinders Z whichare distributed here between two cylinder banks 2, 3; each cylinder hasa combustion chamber with two inlet valves, two outlet valves, a glowplug and a fuel injector, (not illustrated in more detail individually).A first inlet duct 4 and a second inlet duct 5 are assigned to eachcylinder Z and combustion air can be fed to the respective cylinder Zvia said inlet ducts 4 and 5. In this context the correspondingcomponents have been provided with the associated reference symbols onlyfor the first cylinder Z, for the sake of clarity.

The inlet ducts 4, 5 are connected to an air supply duct 6 which iscommon to the cylinder Z of the internal combustion engine 1. Theopening cross section of a respective first inlet duct 4 of an inletduct deactivation device 7 which is common to all the cylinders Z, canbe changed continuously between an open position and a closed position.For this purpose, an adjustable flap is preferably provided. Therespective first inlet duct 4 is preferably embodied as a filling duct,and the second inlet duct 5 is preferably embodied as a swirl duct.

The internal combustion engine 1 receives its combustion air via firstand second air supply lines 8, 9, in each of which an air mass flow ratemeter 10 is arranged. The combustion air of the air supply lines 8, 9 iscompressed by means of respective exhaust gas turbochargers 11, 12 andfed to a charge air cooler 13 for cooling the compressed combustion air.At the outlet end, the charge air cooler 13 is connected via a third airsupply line 14 to the air supply duct 6, with a throttle valve 15 beingarranged in the third air supply line 14.

Exhaust gas generated in the combustion chambers of the cylinders Z isdischarged via exhaust gas lines 16, 17 which are assigned to thecylinder banks 2, 3. In addition, exhaust gas can also be added to thecombustion air via exhaust gas recirculation lines 18, 19 and thereforefed back to the internal combustion engine 1. The proportion of fed backexhaust gas (EGR rate) can be set by means of EGR valves 20, 21 in theexhaust gas recirculation lines 18, 19 and by means of the throttlevalve 15. The exhaust gas which is fed back to the internal combustionengine 1 is preferably temperature controlled by means of an EGR cooler22, but the EGR cooler 22 can also be bypassed (not shown). Optionallycooled or hot exhaust gas can therefore be added to the combustion air.Exhaust gas which has not been recirculated is fed to an exhaust gaspost-treatment system via the exhaust gas turbochargers 11, 12.

A preferred embodiment of the exhaust gas post-treatment system A for aninternal combustion engine 1, illustrated schematically in block form inFIG. 2, comprises (in the direction of flow of the exhaust gas) anoxidation catalytic converter 23, a particle filter 24, an SCR catalyticconverter 25 and a downstream sound damper 26. The latter components arearranged in an exhaust gas line 27, in which the oxidation catalyticconverter 23 is preferably installed close to the internal combustionengine while the SCR catalytic converter 25 is arranged in an underfloorposition with respect to the associated motor vehicle. In order to meterammonia or a reducing agent which is able to release ammonia, a reducingagent metering system 32 is provided. The reducing agent can be fed to ametering nozzle 33 from which it is added to the exhaust gas in a finelydistributed way upstream of the SCR catalytic converter 25.

The exhaust gas line 27 can adjoin one of the respective exhaust gasturbochargers 11, 12 at the internal combustion engine end. In thiscase, the exhaust gas post-treatment system A is provided twice. Howeverit is also possible to provide for the exhaust gas lines 16, 17 to becombined downstream of the exhaust gas turbochargers 11, 12 and for theexhaust gas streams therefore to be fed together to the exhaust gas line27. In this case only a single embodiment of the exhaust gaspost-treatment system A is provided.

Temperature sensors 28, 29, 30, 31, provided in the exhaust gaspost-treatment system A, can be used to sense the temperatures upstreamof the oxidation catalytic converter 23, the particle filter 24 and theSCR catalytic converter 30 and in the bed of the SCR catalyticconverter. In addition, further sensors which are not illustrated inFIGS. 1 and 2, in particular for pressures and temperatures in the linesand components assigned to the exhaust gas post-treatment system A andthe internal combustion engine 1, may be provided.

To operate the internal combustion engine 1 in an optimum way, anelectronic control unit is provided which, on the one hand, receivesinformation about decisive state variables such as, for example,temperatures and pressures from the corresponding sensors and, on theother hand, can output control signals as setting variables to actuatorssuch as, for example, the EGR valves 20, 21 or the inlet ductdeactivation means 7. In particular, the control unit is able to actuatethe fuel injectors in order to carry out multiple injections and to setthe fuel injection pressure according to requirements.

In order to determine the setting variables, the control unit can makeuse of stored characteristic diagrams or calculation routines. In thiscontext, the control unit and the associated inputs and outputs are notillustrated. The control unit is therefore able to set the decisiveoperating parameters on the gas supply side as well as those for thefuel supply as a function of the sensed state variables, and thereforeinfluence the combustion process in the combustion chambers of theinternal combustion engine 1 in a way which is targeted and compatiblewith requirements.

According to the invention, various operating settings are provided foroperating the internal combustion engine 1 economically and with a lowlevel of pollutants. In this case a set of predefined internalcombustion engine operating parameters (which are associated with aspecific operating setting and which have respectively predefinedvalues) corresponds to a specific combustion method which is assigned tothe respective operating setting. If the predefined values for thepredefined internal combustion engine operating parameters (associatedwith a respective operating setting) are set, the correspondingcombustion method becomes active. A changeover from one combustionmethod to another (i.e., from one operating setting into another) isperformed when predefinable switchover criteria are present. Theseswitchover criteria relate essentially to the upward or downwardtransgression of predefinable temperature threshold values of componenttemperatures or operating resource temperatures. A particularlypreferred procedure will be explained below with reference to a statediagram which is illustrated in FIG. 3.

In FIG. 3, BV1, BV1 a, BV2, BV3, BV4 denote various operating settingsor combustion methods, and the changeovers from one combustion method toanother take place according to the indicated arrows. In this context,the switchover criteria which are decisive for a changeover are denotedby T1, T2, T3, T4 and are preferably determined by correspondingtemperature threshold values. The internal combustion engine 1 iscorrespondingly operated as follows.

When there is a cold start of the internal combustion engine 1, a firstheating operating setting or a first heating combustion method BV1(configured for rapid heating of the exhaust gas post-treatment systemA) is first set. Here, a cold start is understood to mean the presenceof a cooled exhaust gas post-treatment system A and/or a cooled coolantwhen the internal combustion engine 1 starts. Temperatures belowapproximately 180° C. are typically present here in the exhaust gaspost-treatment system A, in particular upstream of the particle filter24, and the coolant is typically at temperatures below approximately 50°C.

When the first heating combustion method BV1 is active, thesetemperatures rise quickly and when a first switchover criterion T2 ispresent with BV1 a a second heating operating setting (second heatingcombustion method) is set as a variant of the first heating combustionmethod BV1. When a second switchover criterion T1 is present, awarmed-up state is reached and a changeover to a basic operating setting(basic combustion method) BV2 is carried out. The basic operatingsetting is configured to be significantly more economical in terms offuel compared to the heating combustion method BV1, BV1 a, but permitsfurther slight heating of the exhaust gas post-treatment system A.

The presence of a third switchover criterion T3 characterizes a fullyoperationally capable state of the exhaust gas post-treatment system Aand brings about a changeover into a third combustion method BV3 withthird operating settings, in which case BV3 is configured foroptimization of consumption.

If, due to unfavorable travel conditions, cooling in the exhaust gaspost-treatment system A occurs starting from the basic combustion methodBV2 or the third combustion method BV3, in such a way that predefinablecleaning characteristic values (such as, for example, conversion ofpollutants) are undershot, a fourth switchover criterion T4 is present.In this case, a changeover to a fourth combustion method BV4 with fourthoperating settings takes place, in which case BV4 has an increasedheating effect for the exhaust gas post-treatment system A compared tothe basic combustion method BV2. If sufficient heating occurs due to thesetting of the fourth combustion method BV4, there is a changeover backto the basic operating method BV2 when the second switchover criterionT1 is present.

Preferred refinements of the individual switchover criteria areexplained below.

The first switchover criterion T2 which is decisive for the changeoverfrom the first heating combustion method BV1 to the second heatingcombustion method BV1 a is preferably present if the oxidation catalyticconverter 23 has a minimum conversion capacity in terms of oxidation ofunburnt exhaust gas components. (That is, it has exceeded its light-offtemperature.) This is typically the case if at the inlet end of theparticle filter 24 or at the inlet end of the oxidation catalyticconverter 23 a temperature threshold value of approximately 180° C. isexceeded, which is detected by means of the temperature sensor 29 andthe temperature sensor 28, respectively.

The second switchover criterion T1 which is decisive for the changeoverfrom the second heating combustion method BV1 a to the basic combustionmethod BV2 is preferably present if the SCR catalytic converter 25 has aminimum conversion capacity in terms of nitrogen oxide conversion. (Thatis, it has exceeded its light-off temperature.) This is typically thecase if at the inlet end of the SCR catalytic converter 25 or in the bedof the SCR catalytic converter a temperature threshold value ofapproximately 220° C. is exceeded, which is detected by means of thetemperature sensor 30 and the temperature sensor 31, respectively. Inthis case, the addition of a reducing agent into the exhaust gaspost-treatment system A is enabled. If appropriate, the reducing agentmetering system 32 is correspondingly actuated for immediate metering ofthe reducing agent.

The third switchover criterion T3 which is decisive for the changeoverfrom the basic combustion method BV2 to the combustion method BV3 ispreferably present if the SCR catalytic converter 25 has at leastapproximately reached its maximum conversion capacity. This is typicallythe case if at the inlet end of the SCR catalytic converter 25 or in thebed of the SCR catalytic converter a temperature threshold value ofapproximately 250° C. is exceeded, which is detected by means of thetemperature sensor 30 or temperature sensor 31.

The fourth switchover criterion T4 which is decisive for the changeoverfrom the basic combustion method BV2 or the third combustion method BV3to the fourth combustion method BV4 is preferably present if the SCRcatalytic converter 25 has undershot a predefinable minimum conversioncapacity. This is typically the case if at the inlet end of the SCRcatalytic converter 25 or in the bed of the SCR catalytic converter atemperature threshold value of approximately 210° C. is undershot, whichis detected by means of the temperature sensor 30 and the temperaturesensor 31, respectively. This temperature threshold value is thusslightly below the temperature threshold value which serves asswitchover criterion T1. As a result, a certain hysteresis is providedand excessively frequent switching over, in particular between the basiccombustion method BV2 and the fourth combustion method BV4, is avoided.

As mentioned, the fourth combustion method BV4 is configured for heatingof the exhaust gas post-treatment system A. If this has taken placesufficiently, the basic combustion method BV2 is therefore set again, asillustrated in FIG. 3. The presence of the switchover criterion T1,which has already been explained at the state changeover from the secondheating combustion method BV1 a to the basic combustion method BV2, ispreferably decisive for this.

Preferred refinements of the operating settings (i.e., preferredrefinements of the individual combustion methods) are explained below,the basic combustion method BV2 serving as a starting point. In theexplanation of the other combustion methods, reference is made to theinternal combustion engine operating parameters which are set in thebasic combustion method BV2, and the most important differences areexplained.

The basic combustion method BV2 is preferably configured for lownitrogen oxide (NOx) raw emissions, which permits especially low NOxexhaust end pipe emission values, even when the SCR catalytic converter25 is not optimally effective. It is advantageous for this purpose toset a comparatively late position of the center of combustion. Inparticular, the following fuel injection parameters are preferred. Amain injection and at least one pre-injection which is offset in termsof timing from the main injection are provided. Post-injection isdispensed with. A comparatively late start of the main injection ispreferably set. In the case of a medium internal combustion engine loadand internal combustion engine rotational speed, typical values areapproximately 2° CAaTDC to approximately 6° CAaTDC. A start of maininjection at approximately 4° CAaTDC is particularly preferred here. Astart of injection between 3° CA and 7° CA before the start of the maininjection is preferably set for the at least one pre-injection.

It is particularly preferred, in the basic combustion method BV2, to settwo individual pre-injections which are offset from one another and fromthe main injection. In order to achieve the lowest possible NOx rawemissions, the combustion air which is fed to the internal combustionengine 1 can be enriched comparatively heavily with exhaust gas (i.e.,to set comparatively high exhaust gas recirculation rates (EGR rates)),at least for low load and for a medium load. An EGR rate which decreasesas the load increases, starting from approximately 65% at low load tozero % at full load, is provided, and the recirculated exhaust gases areconducted via the EGR cooler (i.e., a cooled exhaust gas recirculation).With the operating parameters which are set it is possible to achieveoptimum combustion in terms of the formation of NOx, but this is notoptimized thermodynamically so that when a basic combustion method BV2is set a certain degree of heating of the exhaust gas post-treatmentsystem A takes place.

In contrast, the third combustion method BV3 is optimized in terms ofthe consumption of fuel. In comparison with the basic combustion methodBV2, a relatively early start of the main injection is set. A start ofthe main injection in the region of the top dead center or atapproximately 2° CAbTDC is preferred for an average internal combustionengine load and internal combustion engine rotational speed. At the sametime, a reduced EGR rate is set, preferably approximately 25% in thethird combustion method BV3. In addition, for combustion which isimproved in terms of thermodynamics the fuel injection pressure isincreased by 50 bar to 500 bar compared to the basic combustion methodBV2, given comparable load points. In this case, as for the othercombustion methods, a fuel injection pressure which increases as theinternal combustion engine load increases is preferably set. The furthersettings remain preferably unchanged compared to the basic combustionmethod BV2. At least one separate pre-injection is therefore alsopreferably provided for the third combustion method BV3.

In contrast to the third combustion method BV3, the fourth combustionmethod BV4 is aimed at increased heating of the exhaust gaspost-treatment system A. This is achieved by activating a latepost-injection, which preferably does not also burn. Preferably, thestart of post-injection is in the range from 60° CAaTDC up to 160°CAaTDC, with 110° CAaTDC to 150° CAaTDC being particularly preferable.The post-injected fuel is no longer detected by the combustion in thecombustion chamber here and passes essentially without being chemicallychanged, but in a vaporized form, into the exhaust gas. In the exhaustgas post-treatment system, post-combustion can take place, for exampleat the oxidation catalytic converter 23, as a result of which heating isbrought about. An EGR rate of typically 40% to 50%, which is slightlyreduced compared to the basic combustion method BV2, is set as anadditional measure. The further settings preferably remain unchangedcompared to the basic combustion method BV2. At least one separatepre-injection is therefore preferably also provided for the fourthcombustion method BV4.

A heating effect which is increased compared to the fourth combustionmethod BV4 is brought about by the first heating combustion method BV1.As far as the fuel injection parameters are concerned, an individual,offset pre-injection with a start of injection of approximately 5° CAbefore the start of the main injection and a start of main injectionwhich is later compared to the basic combustion method BV2, are set. Astart of main injection at approximately 7° CAaTDC is preferred.

Furthermore, an accumulated or post-injection which also burns iscarried out. This is to be understood as a post-injection with a startof post-injection immediately after, or only a few degrees CA after, theend of the main injection. The post-injected quantity of fuel istherefore detected by the combustion of the main injection.

If the combustion has an effect on torque, the quantity of fuel which isinjected during the main injection is adapted in such a way that thetorque which is output remains as far as possible unchanged andtherefore fluctuations in torque due to a change into the fourthcombustion method are avoided. The quantity of post-injected fuel ispreferably of the order of magnitude of the quantity of fuel in the maininjection here. In addition, in the first heating combustion method BV1an injection pressure which is reduced compared to the basic combustionmethod BV2 is preferably set. An injection pressure reduction byapproximately 30% to 50% is preferred. The EGR rate is preferably givena similar setting to that in the fourth combustion method BV4. In thiscontext, an uncooled exhaust gas recirculation can be provided directlyafter the beginning of the cold start, and switching over to a cooledexhaust gas recirculation can take place after a predefinable exhaustgas temperature has been reached upstream of the oxidation catalyticconverter 23.

If the oxidation catalytic converter 23 has reached its light-offtemperature, a separate, late post-injection of fuel is activated inaddition to the settings of the first heating combustion method BV1, ina way which is analogous to the fourth combustion method BV4. Theactivation of the post-injection typically occurs if the temperature atthe inlet of the oxidation catalytic converter 23 or at the inlet of theparticle filter 24 exceeds approximately 180° C., which is detected byreading in the measured values supplied from the temperature sensors 28,29.

The application of heat into the exhaust gas is increased once morethrough post-oxidation of the unburnt fuel components which are added tothe exhaust gas with the post-injection. As a result, components whichare arranged downstream of the oxidation catalytic converter 23 reachtheir operating temperature quickly. In this case, a changeover to thebasic combustion method BV2 is performed, typically when the temperatureupstream of the SCR catalytic converter 25 or in the bed of saidcatalytic converter exceeds approximately 220° C.

In order to achieve a further increased heating effect in the firstand/or second heating combustion methods, at least temporary heating ofglow plugs which are assigned to the combustion chambers of the internalcombustion engine can be provided. This measure is advantageous inparticular when the engine is comparatively cold, and such measure ispreferably taken if the temperature of the coolant used for cooling theinternal combustion engine drops below a predefinable value of, forexample, 50° C.

However, heating of the glow plugs can be provided even givencorresponding travel conditions when the internal combustion engine iswarmed up. For example, in addition to said settings in the basiccombustion method BV2 and/or in the third combustion method BV3 and/orin the fourth combustion method BV4, it is possible to provide what isreferred to as intermediate heating with heated glow plugs if travelconditions are present in which the internal combustion engine isbecoming cooler or threatens to become cooler. This can be the case, forexample, at a low partial load, in particular in conjunction with lowexternal temperatures.

FIG. 4 illustrates, in diagram form, a temperature profile which isachieved in the exhaust gas post-treatment system A with the methodaccording to the invention compared to a temperature profile for thecontinuously set basic combustion method BV2, together with anassociated travel curve. Here, the travel curve which is denoted by 36gives the velocity v of a motor vehicle which is equipped with theinternal combustion engine 1 and the exhaust gas post-treatment system Aaccording to FIGS. 1 and 2. The line 34 represents the temperatureprofile for the procedure according to the invention with setting of thedifferent combustion methods BV1, BV1 a, BV2, BV3 and BV4 according tothe time segments at which the respectively specified combustion methodis active. (The time segments are designated correspondingly at theupper edge of the diagram.) For comparison, the broken line 35represents a temperature profile such as occurs with the continuouslyset basic combustion method BV2. Here, the lines 34, 35 represent anexhaust gas temperature TSCR which is respectively sensed with thetemperature sensor 30 at the inlet end of the SCR catalytic converter25.

According to the profile of the line 34, the temperature TSCR upstreamof the SCR catalytic converter 25 rises quickly with a short delaystarting from a cold start (t0) when the first heating combustion methodBV1 is set. The rise in temperature continues after the changeover intothe combustion method BV1 a at the time t1 even though the velocity v issimultaneously decreasing. For this reason, the light-off temperature TAof the SCR catalytic converter 25 is reached at a comparatively earlytime t2, and urea solution can be metered into the exhaust gas.Therefore, both a changeover to the basic combustion method BV2, whichis favorable for consumption, and reduction of nitrogen oxide canalready take place at a comparatively early time. When the basiccombustion method BV2 is active, the temperature TSCR continues to riseat moderate velocities v. It is therefore possible to change overrelatively quickly to the combustion method BV3 which is optimized forconsumption after a cold start has taken place at the time t3. At thelow velocities v which occur in the time period between t3 and t4, onlya small amount of heat is applied into the exhaust gas, so that thetemperature TSCR drops. However, the temperature of the SCR catalyticconverter 25 is prevented from dropping below its light-off temperatureTA by virtue of the fact that a changeover to the combustion method BV4with a heating effect occurs at the time t4. In this context, althoughthe velocity v remains low, the temperature of the SCR catalyticconverter 25 increases, so that it returns to the range of its optimumeffectiveness.

In contrast, when the basic combustion method BV2 which is setconstantly it is not possible to achieve satisfactory heating of the SCRcatalytic converter 25, as is shown by a comparison with the temperatureprofile of the line 35. The temperature of the SCR catalytic converter25 exceeds the light-off temperature TA for only a short time, so thatno effective reduction in nitrogen oxide can be achieved. In contrast,the procedure according to the invention permits both low consumption offuel and low emissions of pollutants.

It is possible to provide for deactivation of the inlet duct to beperformed in the partial load range in the warmed-up state as a furthermeasure for improving the combustion profile. The adoption of thismeasure is preferably tied to the presence of a minimum temperature of,for example, 40° C. of the coolant. When the inlet duct deactivation iscarried out, the cross section of, in each case, one inlet duct 4 of thecylinder Z is increasingly reduced by means of a flap as the internalcombustion engine load decreases. The inlet duct deactivation ispreferably activated in a load range below approximately 50% of therated load. This measure increases the swirl of the combustion airflowing into the cylinder Z of the internal combustion engine 1 andtherefore reduces the consumption of fuel and the raw emissions.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1.-12. (canceled)
 13. A method for operating an air-compressingfuel-injection internal combustion engine having an exhaust gaspost-treatment system that includes a particle filter and a nitrogenoxide reduction catalytic converter, wherein said method includesprovisions for a plurality of internal combustion engine operatingsettings, with respective predefined values for predefined internalcombustion engine operating parameters, said method comprising: when theinternal combustion engine is warming up, setting a heating operatingsetting; when the internal combustion engine is in a warmed-up state,setting a basic operating setting; and when the temperature in theexhaust gas post-treatment system exceeds a predefinable first thresholdvalue, changing from the heating operating setting to the basicoperating setting; wherein when the internal combustion engine is in thewarmed-up state, at least a third operating setting, with an exhaust gasrecirculation rate that is reduced compared to the basic operatingsetting, can be set, in addition to the basic operating setting.
 14. Themethod as claimed in claim 13, wherein the internal combustion engine isoperated with a compression ratio of less than 19:1, at least at one ofthe operating settings which are set in the warmed-up state.
 15. Themethod as claimed in claim 13, wherein: the first threshold value is atemperature value at which the nitrogen oxide reduction catalyticconverter becomes effective; and an additive for nitrogen oxidereduction is added to the internal combustion engine exhaust gas in thewarmed-up state upstream of the nitrogen oxide reduction catalyticconverter.
 16. The method as claimed in claim 13, wherein, when theheating operating setting is active and the temperature in the exhaustgas post-treatment system exceeds a predefinable second threshold value,a separate fuel post-injection is activated.
 17. The method as claimedin claim 16, wherein the second threshold value is a temperature valueat which an oxidation catalytic converter which is connected upstream ofthe particle filter becomes effective.
 18. The method as claimed inclaim 13, wherein, when the heating operating setting or the basicoperating setting is active, the fuel injection comprises at least oneseparate pre-injection.
 19. The method as claimed in claim 13, wherein,at least when the basic operating setting is active, double fuelpre-injection is performed.
 20. The method as claimed in claim 13,wherein, when the heating operating setting is active, a fuel injectionpressure that is reduced compared to the basic operating setting is set.21. The method as claimed in claim 13, wherein, when said thirdoperating setting is active, a fuel injection pressure is set which isincreased compared to the basic operating setting.
 22. The method asclaimed in claim 13, wherein: in the warmed-up state, a fourth operatingsetting is provided; in the fourth operating setting, at least one of alate fuel post-injection and a reduced exhaust gas recirculation rate isimplemented.
 23. The method as claimed in claim 13, wherein, in at leastone of the operating settings for the warmed-up state, an at leasttemporary inlet duct deactivation is implemented.
 24. The method asclaimed in claim 13, wherein, in at least one of the operating settingsfor the warmed-up state, a glow plug which is assigned to a combustionchamber of the internal combustion engine is heated, at leasttemporarily.